Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Base stations may communicate with mobile devices on downstream and upstream links. Each base station has a coverage range, which may be referred to as the coverage area of the cell. In some cases the coverage area may be subdivided into multiple cells. Also, in some cases, a base station may transmit multiple component carriers on different portions of available spectrum. These component carriers may also be referred to as cells.
A user equipment (UE) may be served by more than one carrier. In some cases a UE may be served by multiple carriers transmitted from a single base station (e.g., in a carrier aggregation mode); in other cases, a UE may be served by multiple carriers transmitted from more than one base station (e.g., a dual connectivity mode). The number of carriers that may serve the UE may be limited by the available bandwidth spectrum and the capabilities of the control channel signaling, such as a physical uplink control channel (PUCCH).